The invention relates to a magnetic head having a core of a magnetic material which includes two spaced-apart core parts each having a width which is larger than the width of a recording/playback track, between which core parts a gap is formed the width of which is defined by first and second indentations extending from the respective side edges of the core parts.
Such a magnetic head is known from U.K. Patent Specification No. 1.593,310.
Magnetic recording and playback techniques have of late made significant progress, in particular in connection with improvement of the techniques for recording signals of extremely high frequencies as they are used in video recorders.
As is known, the video signal can be written on a magnetic tape in oblique tracks by means of two magnetic heads moving at high speed. In the VIDEO 2000 system, this is done by passing the tape at a speed of 2.44 cm/s in the form of a helix over 186.degree. around a drum. The part of the drum to which the two magnetic heads present diametrically opposite to each other are connected, rotates at a circumferential speed of 5.08 m/s. In order to avoid, as far as the luminance signal is concerned, cross-talk between two tracks written one after the other, the gaps of the magnetic heads, which (viewed in the direction of movement) are 0.5 .mu.m long and approximately 22 .mu.m wide, are not placed perpendicular to the direction of movement. In fact, each gap makes an angle of 15.degree. (the azimuth angle) with the normal to the direction of movement, the two writing gaps being shifted in opposite directions. As a result of this the tracks can be written on the tape without intermediate space.
Because it is undesirable both from a point of view of magnetic reluctance and from a point of view of handleability and mechanical rigidity to give the core of a video head a width which corresponds to the width of a video track (in the VIDEO 2000 system this width is slightly less than 22.6 .mu.m), it is usual to make the core thicker (for example 150 .mu.m) and to make indentations at the area of the gap in the edges of the core, which indentations between them define a gap of the desired width. The indentations can be made in known manner by means of laser methods or ion beam etching. A disadvantage of such a head construction is that the adhesion of the two core parts at the area of the tape contact face is produced only by the bonding means (usually glass) in the remaining part of the gap which has a width of a few tens of microns and a height of a few tens of microns. Although it is possible to also fill the indentations afterwards with glass, this has for its disadvantage that a second "glass bonding" process is necessary while moreover a type of glass having a lower softening temperature and an associated lower resistance to detrition than the glass in the gap are to be used.
Otherwise, whether the indentations are filled with glass or not, it is a disadvantage in both cases that, upon making the indentations which are large with respect to the dimensions of the gap, the positions of the ends of the gap are not exactly reproducible. The gap definition thus is not optimal.